The inquiry heard the risk of carbon monoxide poisoning at mine fires was known following a 2006 fire, but when the blaze started on February 9 the Country Fire Authority was yet to implement a 2010 draft operating procedure.

Mr Lapsley said it should have been signed off and published earlier.

He was also pressed on why firefighters were not given breathing apparatuses after it was agreed they should be compulsory when entering the mine.

Mr Lapsley said protocols were set around the use of breathing apparatuses in consultation with firefighters who did their own "dynamic risk assessment".

"It was found to be totally impractical to actually wear a breathing apparatus all the time," Mr Lapsley said.

He was also questioned on the possibility of the fire starting within the mine, which he said he could not rule out but was unlikely.

"The probability of having a fire start within the mine from some vehicle movement, mechanical device or other things, you couldn't actually take away," Mr Lapsley said, adding there was no evidence of fires starting from any way other than ember attacks.